Adaptive Changes in Color Vision from Long-Term Filter Usage in Anomalous But Not Normal Trichromacy

Abstract

For over 150 years, spectrally selective filters have been proposed to improve the vision of observers with color vision deficiencies [1]. About 6% of males and <1% of females have anomalies in their gene arrays coded on the X chromosome that result in significantly decreased spectral separation between their middle- (M-) and long- (L-) wave sensitive photoreceptors [2]. These shifts alter individuals’ color-matching and chromatic discrimination behavior such that they are classified as anomalous trichromats [3,4]. Broad-band spectrally selective filters proposed to improve color vision of observers with color vision deficiencies principally modify the illuminant and are largely ineffective in enhancing discrimination or perception because they do not sufficiently change the relative activity of M- and L-photoreceptors [5,6]. Properly tailored notch filters, by contrast, might increase the difference of anomalous M- and L-cone signals. Here, we evaluated the effects of long-term usage of a commercial filter designed for this purpose on luminance and chromatic contrast response, estimated with a signal detection-based scaling method, We found that continuous use over two weeks was accompanied by increased chromatic contrast response in anomalous trichromats. Importantly, these improvements were observed when tested without the filters, thereby demonstrating an adaptive visual response. Normal observers and a placebo control showed no such changes in contrast response. These findings demonstrate adaptive increases in chromatic response due to long-term usage of a notch filter in observers with reduced spectral discrimination. They invite the suggestion that modifications of photoreceptor signals activate a plastic postreceptoral substrate that could potentially be exploited for visual rehabilitation.